The present invention relates to polyurethane foams. In particular, the present invention relates to a polyurethane foam-forming reaction mixture possessing a silicone copolymer surfactant, methods for making the surfactant, and a process for preparing low density polyurethane foams.
Polyurethane foam is typically prepared by generating a gas during polymerization of a liquid reaction mixture generally comprised of a polyester or polyether polyol, a polyisocyanate, a surfactant, catalysts, one or more blowing agents and other auxiliary agents. The gas causes foaming of the reaction mixture to form a cellular structure. The surfactant stabilizes the polyurethane foam structure.
In current polyurethane technology silicone surfactants are used to assist and control nucleation sites for polyurethane foam cell formation, compatibilization of the chemical components and stabilization of cells in the developing polyurethane foam.
Flexible polyurethane foams are commercially prepared as slabstock foam or in molds. Some slabstock foam is produced by pouring the mixed reactants in large boxes (discontinuous process), while other foam is prepared in a continuous manner by deposition of the reacting mixture on a paper lined conveyor. The foam rises and cures as the conveyor advances and the foam is cut into large blocks as it exits the foam machine. Some of the uses of flexible slabstock polyurethane foams include: furniture cushions, bedding, and carpet underlay.
Flexible foam formulations usually include e.g., a polyol, a polyisocyanate, water, optional blowing agent (low boiling organic compound or inert gas, e.g., CO2), a silicone type surfactant, and catalysts. Flexible foams are generally open-celled materials, while rigid foams usually have a high proportion of closed cells.
Polyurethane foams are produced by reacting a di- or polyisocyanate with compounds containing two or more active hydrogens, optionally in the presence of blowing agent(s), catalysts, silicone-based surfactants and other auxiliary agents. The active hydrogen-containing compounds are typically polyols, primary and secondary polyamines, and water. Two major reactions are promoted by the catalysts among the reactants during the preparation of polyurethane foam, gelling and blowing. These reactions must proceed simultaneously and at a competitively balanced rate during the process in order to yield polyurethane foam with desired physical characteristics.
Reaction between the isocyanate and the polyol or polyamine, usually referred to as the gel reaction, leads to the formation of a polymer of high molecular weight. This reaction is predominant in foams blown exclusively with low boiling point organic compounds. The progress of this reaction increases the viscosity of the mixture and generally contributes to crosslink formation with polyfunctional polyols. The second major reaction occurs between isocyanate and water. This reaction adds to urethane polymer growth, and is important for producing carbon dioxide gas which promotes foaming. As a result, this reaction often is referred to as the blow reaction.
Historically, numerous grades of polyurethane foams were blown with chlorofluorocarbon (CFC) based blowing agents to reduce foam density, control foam firmness, and cool the foams to minimize discoloration, degradation, and possible foam ignition. Environmental issues regarding ozone depletion in connection with certain CFC's has led to the Montreal Protocol, CFCs. As a result, the polyurethane foam industry has tried to achieve the same foam grades and quality produced using alternate blowing agents (ABAs). Many different ABAs have been evaluated in flexible foam including alkyl carbonates, acetone, methylene chloride, carbon tetrachloride, trichloroethane and pentanes. Recently, supplemental added inert gases such as carbon dioxide (CO2) have been effectively employed as part of the blowing agent for flexible polyurethane foams.
Currently silicone surfactants are used to emulsify, nucleate and stabilize the polyurethane foam. This is well known in the literature. The silicone surfactants currently used for a variety of applications, contain for example, either all ethylene oxide polyether pendants reacted to the siloxane copolymer backbone or all ethylene oxide/propylene oxide pendants.
Low density slabstock polyurethane foams are produced widely, and economical methods of producing such foams include using large amounts of blowing agents and fillers. However, the increased levels of auxiliary blowing agent and water used in the production of low density flexible slabstock polyurethane foam cause inner foam splits or collapse. Also, the use of increased levels of inorganic fillers for the production of slabstock polyurethane foams, often results in inner foam splits and coarse cell structure.
Prior art silicone surfactants used in the preparation of low density polyurethane foams can cause coarse cell structure and/or show low potency, (especially when density is less than 10 kg/m3). Also, conventional silicone surfactants used to prepare polyurethane foams having large quantities of fillers, i.e., more than 50 weight percent of polyols, can present production problems, e.g., foam collapse and coarse cells. Thus, not all silicone surfactants are suitable for these foam systems. As such, high potency silicone surfactants are required to stabilize the foam composition until the product-forming chemical reaction completes sufficiently, the foam is self-supporting, and it does not suffer objection-able collapse and coarse cells. Silicone surfactants of this invention can provide more uniform and finer cells, and have more stable foaming processing than other current commercial surfactants.
The present invention provides polyurethane foams with silicone surfactants and addresses the problem of coarse cell structure and/or low surfactant potency.